A toner binder for electrophotography for a heat fixing system, which is a fixing system of images commonly applied in copiers, printers and the like, is required to allow a toner not to fuse to a hot roller even at a high fixing temperature (hot offset resistance), to be capable of fixing a toner even at a low fixing temperature (low-temperature fixing property), to have storage stability as microparticles (blocking resistance), and the like.
In order to improve such fixing performances of a toner, it is conventionally known to use incompatible resins specialized in a low temperature range and a high temperature range as a matrix phase and a domain phase, respectively. In addition, there is proposed a method in which a compatibilizing agent for compatibilizing the incompatible resins is contained in a vinyl resin such as a styrene type polymer (Patent Document 1 and the like).
In order to improve blocking resistance, especially blocking resistance in relation to storage stability under a high-temperature and -humidity environment, there is proposed a toner binder composed of a polyester resin obtained by using a specific polyol component such as 1,2-propylene glycol and neopentyl glycol, without consideration for the SP value range and the HLB value range (Patent Document 2 and the like).